Core-shell lithium transition metal oxides

Abstract

A lithium transition metal oxide powder for use in a rechargeable battery is disclosed, where the surface of the primary particles of said powder is coated with a LiF layer, where this layer consists of a reaction product of a fluorine-containing polymer and the primary particle surface. The lithium of the LiF originates from the primary particles surface. Examples of the fluorine-containing polymer are either one of PVDF, PVDF-HFP or PTFE. Examples of the lithium transition metal oxide are either one of —LiCo d MeO 2 , wherein M is either one of both of Mg and Ti, with e<0.02 and d+e=1; —Li 1 + a M′ 1−a O 2±b M 1 k S m with −0.03<a<0.06, b<0.02, M′ being a transition metal compound, consisting of at least 95% of either one or more elements of the group Ni, Mn, Co and Ti; M 1 consisting of either one or more elements of the group Ca, Sr, Y, La, Ce and Zr, with 0≦k≦0.1 in wt %; and 0<m<0.6, m being expressed in mol %; and —Li a Ni x CO y M″ z O 2±e A f , with 0.9<a′<1.1, 0.5≦x≦0.9, 0<y≦0.4, 0<z≦0.35, e<0.02, 0≦f≦0.05 and 0.9<(x+y+z+f)<1.1; M″ consisting of either one or more elements from the group Al, Mg, and Ti; A consisting of either one or both of S and C.

The invention claimed is: 
     
       1. A lithium transition metal oxide powder for use in a rechargeable battery, the powder comprising primary particles having a surface coated with a LiF coating layer, wherein the LiF coating layer is the reaction product of a fluorine-containing polymer and the surface of the uncoated primary particle, and wherein the lithium transition metal oxide powder has a soluble base content, determined by pH titration, that is less than 60% of the soluble base content of a lithium transition metal oxide powder having uncoated primary particles, wherein said LiF coating layer has a thickness of at least 0.5 nm. 
     
     
       2. The lithium transition metal oxide powder of  claim 1 , wherein the soluble base content of the lithium transition metal oxide powder is less than 50% of the soluble base content of a lithium transition metal oxide powder having uncoated primary particles, as determined by pH titration. 
     
     
       3. The lithium transition metal oxide powder of  claim 1 , wherein the surface of the lithium transition metal oxide powder is substantially free of lithium hydroxide and lithium carbonate. 
     
     
       4. The lithium transition metal oxide powder of  claim 1 , wherein the lithium transition metal oxide is selected from the group consisting of
 LiCo d M e O 2 , wherein M comprises one or both of Mg and Ti, with e<0.02 and d+e=1; 
 Li 1+a M′ 1−a O 2±b  M 1   k S m  with −0.03<a<0.06, b<0.02, wherein M′ is a transition metal compound, wherein at least 95% of M′ is selected from the group consisting of Ni, Mn, Co, Mg and Ti; and M 1  comprises one or more elements selected from the group consisting of Ca, Sr, Y, La, Ce and Zr, with 0≦k≦0.1 in wt %; and 0≦m≦0.6, m being expressed in mol %; and 
 Li a′ Ni x Co y  M″ z  O 2±e  A f , with 0.9<a′<1.1, 0.5≦x≦0.9, 0<y≦0.4, 0<z≦0.35, e<0.02, 0≦f≦0.05 and 0.9<(x+y+z+f)<1.1; wherein M″ comprises one or more elements selected from the group consisting of Al, Mg, and Ti, and A comprises one or both of S and C. 
 
     
     
       5. The lithium transition metal oxide powder of  claim 4 , wherein M′=Ni a″ Mn b″ Co c″ , with a″>0, b″>0, c″>0 and a″+b″+c″=1; and a″/b″>1. 
     
     
       6. The lithium transition metal oxide powder of  claim 5 , wherein 0.5≦a″≦0.7, 0.1<c″<0.35, and a″+b″+c″=1. 
     
     
       7. The lithium transition metal oxide powder of  claim 1 , wherein the LiF coating layer has a thickness of at least 0.8 nm. 
     
     
       8. The lithium transition metal oxide powder of  claim 7 , wherein the LiF coating layer has a thickness of at least 1 nm.